I think creating several forums with only specific purposes is not a good idea.
Such a practice would result in a bunch of forums, many of which have some degree of overlaps.
This will cause an extra effort for finding a particular topic.
Even now there are at least 3 forums devoted to integrals (definite/improper/residue), which is unnecessarily distracting for me.
Honestly, It's discouraging that Prophp BB system does not support tags...